1. Field of the Invention
This invention relates to an improvement of a composite type vibration damping material made up of a constraining plate and a viscoelastic material layer laminated on a plate surface of the constraining plate.
2. Description of the Prior Art
Heretofore, composite type vibration damping materials made by using a thin steel plate as a constraining plate and by providing a viscoelastic material layer of rubber, resin or other material on a surface of the constraining plate have been used in various industrial fields. The composite type vibration damping material have been intended to absorb vibrations by virtue of the "dynamic viscoelastic behavior" of the viscoelastic material. From a structural viewpoint, they are roughly divided into two types: a free-layer type made by providing a viscoelastic material layer 2 on a plate surface of a vibrating body 4 as shown in FIG. 7; and a constrained type made by sandwiching a viscoelastic material layer 2 between a vibrating body 4 and a constraining plate 1 or between two constraining plates 1 as shown in FIG. 8. The former absorbs vibrations by converting vibration energy into thermal energy as a result of tension-compression deformation of the viscoelastic material layer. The latter absorbs vibrations by converting vibration energy into thermal energy mainly as a result of shear deformation.
The composite type vibration damping material, either of the free-layer type or of the constrained type, has a viscoelastic characteristic inherent to the viscoelastic material layer. It is considered most serious drawbacks of the composite type vibration damping material that the vibration damping property (loss factor) has a sharp peak near the glass transitional temperature, and that the temperature range for sufficient performance of the vibration damping property is very narrow, which means its dependency on temperature is great.
Heretofore, the following three approaches have been proposed for reducing the temperature dependency of the composite type vibration damping materials: